The present invention relates to a golf ball material which has an excellent thermal stability, processability and flow, enabling high-performance golf balls endowed with a good durability and scuff resistance to be obtained therefrom. The invention also relates to a golf ball that includes as an essential component a molding made from such a golf ball material, and to a method for preparing such a golf ball material.
In recent years, ionomer resins have been widely used as cover materials for golf balls. Ionomer resins are ionic copolymers composed of an olefin such as ethylene and an unsaturated carboxylic acid such as acrylic acid, methacrylic acid or maleic acid, in which some of the acid groups are neutralized with metal ions such as sodium, lithium, zinc or magnesium. These resins provide excellent characteristics in terms of ball durability, rebound resilience and scuff resistance.
Today, the base resins used in golf ball cover materials are predominantly ionomer resins, but a variety of modifications are being made to cope with the constant desire of the users for golf balls which have an excellent thermal stability, durability and scuff resistance.
For example, to improve the heat resistance and scuff resistance of ionomer cover materials, cover materials obtained by blending an ionomer resin with a polyamide having a heat resistance and a high hardness have been described (e.g., Patent Document 1: U.S. Pat. No. 6,353,058; Patent Document 2: U.S. Pat. No. 6,380,349; Patent Document 3: U.S. Pat. No. 6,486,250; Patent Document 4: U.S. Pat. No. 6,774,184; and Patent Document 5: U.S. Pat. No. 6,800,690.
However, in these prior-art publications, as the amount of the polyamide constituent increases, and particularly as the polyamide constituent becomes the matrix, it is inevitably necessary to set the injection molding temperature higher. As a result, thermal deterioration of the ionomer, which has a poor heat resistance, is readily induced, which tends to dramatically lower the physical properties of the molded parts.
Ternary polyamide materials having a good flowability with a low melting point have recently been disclosed for the purpose of improving processability (e.g., Patent Document 6: U.S. Pat. No. 4,992,515; Patent Document 7: JP-A 3-106646; Patent Document 8: JP-A 8-225644; Patent Document 9: JP-A 11-71455; and Patent Document 10: JP-A 2006-111763.
However, when materials prepared by melt-blending such ternary polyamides and ionomers are used in golf balls, the balls tend to have a very poor durability, which is a defect attributable to the polyamide blend material.
Patent Document 1:U.S. Pat No. 6,353,058Patent Document 2:U.S. Pat No. 6,380,349Patent Document 3:U.S. Pat No. 6,486,250Patent Document 4:U.S. Pat No. 6,774,184Patent Document 5:U.S. Pat No. 6,800,690Patent Document 6:U.S. Pat No. 4,992,515Patent Document 7:JP-A 3-106646Patent Document 8:JP-A 8-225644Patent Document 9:JP-A 11-71455Patent Document 10:JP-A 2006-111763